1. Field of the Invention
The present invention relates to sutures used by ophthalmologists to close corneal incisions and more particularly to a system for determining the tension in sutures in order to control corneal astigmatism.
2. Description of the Prior Art
James P. Gills, opthalmologist, M.D., in his publication, entitled "The Effect of Cataract Sutures on Postoperative Astigmatism", published in Volume 51, February, 1974 issue of the American Journal of Optometry and Physiological Optics on pages 97-100, states that with the advent of microsurgery, cataract wound closure has undergone a great transition. A tight cataract wound closure without flat anterior chamber or iris prolapse is desirable. Control of postoperative astigmatism has importance to those interested in the optical care of aphakic patients. James P. Gills used a Bausch & Lomb keratometer to take preoperative readings and postoperative readings for each patient and he then averaged the readings for each type of suture used in the wound closure. James P. Gills summarized his results with the statement that loose cataract wound closure gave against the rule astigmatism and tight cataract wound closure gave with the rule astigmatism. It is therefore evident that an accurate method of controlling tension in the suture would reduce postoperative astigmatism.
Richard C. Troutman, ophthalmologist, M.D., in his publication, entitled "Microsurgical Control of Corneal Astigmatism in Cataract and Keratoplasty", published in Volume 77, September-October, 1973 issue of the Transactions of the American Academy of Ophthalmology and Otolaryngology on pages OP-563-OP-572, states that in cataract surgery the first goal is to develop an incision and closure which would produce a standard or no deviation of astigmatism from the preoperative level. He also states that cataract incisions closed with silk or catgut suture produced an average of 1.50 D (diopter) astigmatism against the rule. Flattening of the vertical steeper meridian and a corresponding steepening of the flatter horizontal meridian occur in 91% of cases when preoperative and postoperative kerometer measurements are compared. He further states that with microsugically deeply placed monofilament suture in an opposing continuous pattern, corneal keratometer readings can be stabilized to preoperative levels. The purpose of the opposing continuous pattern is to equalize tension within the suture. There is no method in the prior art to determine the relative tension in each stitch.
S. S. Barner, opthalmologist, M.D., in his publication, entitled "Surgical Treatment of Corneal Astigmatism", published in Volume 7, Number 1, Spring, 1976 issue of Ophthalmic Surgery on pages 43-48, states that a quantative surgical keratometer was mounted on an operating microscope in order to visualize changes in corneal curvature by J. L. Barraquer (see V Symposium of International Ophthalmic Microsurgery Study Group, London, 1974). This instrument offers the possibility of reading the amount and axis of astigmatism produced and adjusting the sutures accordingly. A somewhat similar qualitative surgical keratometer was constructed by Richard C. Troutman and described in Volume I of his book Microsurgery of the Anterior Segment of the Eye. The Troutman Operating Keratometer identifies the curvatures of the front of the eye, the cornea, during the operation. Prior to the development of the Troutman Operating Keratometer there was no way to monitor the development of surgical procedures during the surgical procedures. The ophthalmologist was only able to measure the curvature of the front of the eye before and after the surgical procedure with a keratometer. This operating keratometer measures qualitatively and not quantatively in that it only measure the variations from the normal standard previously set by the ophthalmologist. The advantage of this operating keratometer over a standard keratometer is that it reads all of the meridians with and against the rule at the same time. It does this by using a reticule placed in the microscope so that the ophthalmologist can compare the difference in all of the meridians in the aspect. I. Robertson in an article in Volume 2, Number 3, 1974, of the Australian Journal of Ophthalmology on page 152 has suggested the use of an illuminated Placido disc mounted on the microscope. The difficulty with both of these methods is that they are basically qualitative instruments and are not easily calibrated so that they reduce postoperative astigmatism. Furthermore the use of a keratometer requires that the ophthalmologist remove the air bubble within the eye before he takes his measurement. The air bubble is essential in keeping the cornea away from the lens which has been implanted.
U.S. Pat. No. 3,994,027, entitled Prepupillary Lens for Implanting in a Human Eye, issued to Ronald P. Jensen and James Fetz on Nov. 30, 1976 teaches a prepupillary lens which may be surgically implanted into a human eye. Similar lenses are discussed in an article by Cornelius D. Binkhorst, M.D., entitled "The Iridocapsular (Two-loop) Lens and the Iris-clip (Four-loop) Lens in Pseudophakia, published in 1973 September-Ocotber edition of Transactions of the American Academy of Ophthalmology and Otolaryngology. All of these lenses require a corneal incision and a corneal wound closure. It would be very beneficial to a patient undergoing a lens implant if the implant surgeon had a tighter control on the tension in each stitch of the suture than he presently has with an operating keratometer.
The inventors have discovered that if the corneal wound closure is too loose the cornea will leak fluids and that if the corneal wound closure is too tight postoperative astigmatism will occur. Since wound closure is dependent on the tension in the stitch of the suture the inventors investigated several methods of measuring the tension. There was one constraint in that they both felt that the measurement of the tension must not interfere with the surgical operation.